A Democratic senator requested Friday that the FBI open a perjury investigation into Homeland Security Secretary Kirstjen Nielsen, accusing her of lying about the Trump administration’s family separation policy during sworn testimony to Congress.

Sen. Jeff Merkley (D-Ore.) released a previously undisclosed memo Thursday from high-level officials at the Department of Homeland Security and the Justice Department in 2017 that outlined policy options to deal with illegal immigration at the border. The second item on the list is a policy to “separate family units.” The memo also notes that an upshot of such policies will be the “substantial deterrent effect.”

Nielsen has long denied there was a policy to separate families; during testimony in front of Congress in December, she said, “We’ve never had a policy for family separation.”

“Compelling new evidence has emerged revealing that high-level Department of Homeland Security officials were secretly and actively developing a new policy and legal framework for separating families as far back as December 2017,” Merkley wrote in a letter to FBI Director Christopher A. Wray. “In light of these conflicting facts, the FBI should immediately investigate whether Secretary Nielsen’s statements violate 18 U.S. Code § 1621, 18 U.S.C § 1001, or any other relevant federal statutes that prohibit perjury and false statements to Congress.”

Katie Waldman, a DHS spokeswoman, blasted Merkley’s claims in a statement Friday night, saying the administration’s role in the family separations has been explained repeatedly to Congress.

Waldman said Nielsen had rejected the policy proposal to separate all families in DHS custody.

“As Secretary Nielsen has said publicly and testified multiple times, DHS has never had a blanket policy of separating families in custody,” Waldman said. “What this pre-decisional, pre-deliberative memo — as well as previously leaked pre-decisional, pre-deliberative documents — shows is that the Secretary was provided a menu of options to prevent the humanitarian crisis we predicted at that time and which has manifested itself today.”

Instead, the administration opted for a “zero tolerance” immigration policy, in which undocumented adults who crossed the border have been routinely prosecuted criminally, which makes the removal of their children an inevitable result, as children cannot be incarcerated in adult facilities. The federal government separated nearly 3,000 children from their parents last year as a result of these new practices.

Nielsen sought to blame the media for the crisis that ensued at the time.

“This misreporting by Members, press & advocacy groups must stop. It is irresponsible and unproductive,” she said in a statement on Twitter in June. “We do not have a policy of separating families at the border. Period.”

The memo makes clear that administration officials had an idea of the backlash the policies around families at the border would create.

“Advocacy groups are aware that this policy shift may occur and therefore are seeking to identify families who have been separated in order to bring a class-action lawsuit,” it read.

This week, a report from the inspector general for the Department of Health and Human Services, which has been responsible for caring for the children after they are separated, said that thousands more children than were previously reported were probably taken from their parents or guardians by immigration agents since Trump took office.

“Although previous administrations also separated minors at the border in some instances — usually when they suspected the child was smuggled, or if the parent appeared unfit — the report said the practice appears far more common under Trump and began nearly a year before administration officials publicly acknowledged it,” The Washington Post’s Amy Goldstein reported.